Routine CI and EI mass spectra of many thermally labile biomedical compounds contain no (M plus H) or M ions for molecular weight determination. The presumption has frequently been that these compounds decompose thermally rather than volatilize as the original molecules. FD mass spectra of many thermally labile compounds frequently contain M or (M plus H) ions but few structurally useful fragment ions. Presumably the stable M or (M plus H) ions are produced from molecules adsorbed on a metal surface and volatilization is not a necessary intermediate step in ion production. It has been possible to obtain CI spectra of thermally labile compounds by direct source insertion techniques which suggest that sample ions are formed from sample molecules on surfaces. These spectra contain abundant (M plus H) ions as well as structurally useful fragment ions. These spectra are very sensitive to the precise details of sample introduction: nature of surface, temperature of surface, position of sample, walls of source, reagent gas. It is proposed to investigate the effects of experimental parameters on the CI spectra of thermally labile biomedical compounds introduced into the ionization region on a surface, to see if the effects are compatible with a model of ionization of adsorbed rather than gaseous species, and to see if the technique can be made reproducible and generally useful for characterization of thermally labile compounds of biomedical interest.